Our laboratory has adapted a primary culture system of cells dissociated from embryonic mouse brain to a form suitable for studying myelinogenesis in vitro. The ontogenic patterns of biochemical parameters in these cultures closely mimic the developmental patterns of these parameters in the intact animal. The culture system responds to a number of regulators of myelinogenesis. Thyroid hormone, glucocorticoids, cell surface adhering lectins, neurotransmnitters, drugs, and insulin all produce specific morphological and biochemical changes. The culture system enables us to study the mechanism of action of both beneficial and detrimental (drugs, etc.) effectors within cells of the central nervous system at a level of sophistication not previously possible. Our future work will include investigations on the regulation of the enzymes associated with the demyelinating diseases, metachromatic leucodystrophy (MCL) and subacute combine degeneration (SCD). Under the auspices of the current grant we found that hydrocortisone inhibits arylsulfatase A (the MCL-associated enzyme) and thyroid hormone is required for the expression of the methylation of myelin basic protein (the SCD-associated reaction). How these hormones function at these specific, important biochemical reactions is the subject that occupies a significant portion of our proposal. In addition, we shall use the primary culture system to investigate the regulation of the synthesis of the myelin associated plasmalogens; an area of neurochemical regulation that has been neglected for too long.